Listen to Bigsby... All you need is fans EXTRACTING air. This creates what is called negative pressure inside your tent. This means that the force of the air being EXTRACTED will draw fresh air in. Having fans that push air into your tent is much less effective. Just open a couple of the flaps on the bottom of the tent and the fresh air will rush right in.

By doing this it removes the hot air inside the tent and also replaces the air for the plants. Negative pressure... look it up.